package algotithm.interview.声网.test2;

import java.io.*;
import java.util.HashMap;

/**
 * @author zhouyanxiang
 * @Date 2021-03-2021/3/31-20:30
 */
public class Main {

    public static void main(String[] args) throws IOException {
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
        BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(System.out));

        String s = reader.readLine();
        char[] c = s.toCharArray();
        HashMap<Character, Integer> map = new HashMap<>(1024);
        for (int i = 0; i < c.length; i++) {
            map.put(c[i],map.getOrDefault(c[i],0) + 1);
        }
        for (int i = 0; i < c.length; i++) {
            if (map.get(c[i]) == 1) {
                writer.write(c[i] + "\n");
                break;
            }
        }
        writer.flush();
        writer.close();
        reader.close();
    }

}
